Process for treating cast iron

ABSTRACT

A PROCESS FOR TREATING LIQUID IRON COMPRISING INTRODUCING AT LEAST ONE METALLIC INOCULATION PRODUCT, SUCH AS PURE MAGNESIUM, CERIUM, SODIUM, CALCIUM OR OTHER METAL OR METAL ALLOY, AT THE BOTTOM OF A BATH OF IRON BY MEANS OF AN IMMERSED BELL, WHEREIN SAID METALLIC INOCULATING PRODUCT IS INTRODUCED INTO THE BATH OF IRON IN THE FORM OF AT LEAST ONE PIECE OF SAID PRODUCT TOTALLY COVERED WITH A COATING OF REFRACTORY MATERIAL, A PART OF THE COATING BEING THINNER THAN THE REST OF THE COATING.

Aug. 10, 1971 H. JARYSTA 3,598,575

PROCESS FOR TREATING CAST IRON Filed April 29, 1968 2 Sheets-Sheet 1 INVEIYT R mmym Aug. 10, 1971 H. JARYSTA PROCESS FOR TREATING CAST IRON 2 Sheets-Sheet 2 Filed April 29, 1968 United States Patent 3,598,575 PROCESS FOR TREATING CAST IRON Henri Jarysta, Pont-a-Mousson, France, assignor to Centre de Recherches de Pont-a-Mousson, Pout-a- Mousson, France Filed Apr. 29, 1968, Ser. No. 724,960 Claims priority, application France, May 9, 1967, 105,658; Mar. 4, 1968, 142,187 Int. Cl. C22c 33/00 U.S. Cl. 75-130 9 Claims ABSTRACT OF THE DISCLOSURE A process for treating liquid iron comprising introducing at least one metallic inoculation product, such as pure magnesium, cerium, sodium, calcium or other metal or metal alloy, at the bottom of a bath of iron by means of an immersed bell, wherein said metallic inoculating product is introduced into the bath of iron in the form of at least one piece of said product totally covered with a coating of a refractory material, a part of the coating being thinner than the rest of the coating.

The present invention relates to the treatment of cast iron and more particularly to the introduction into the liquid iron of an-inoculating metal for the purpose of obtaining a spheroidal graphite cast iron.

It is known that the reaction of a very volatile inoculating metal, such as magnesium, with the iron in which it is introduced is very rapid and very violent and the yield or the result is poor if precautions are not taken for controlling this reaction.

Various known processes tend in fact to control this reaction, lessen the violence and improve the yield.

Thus a process is known which comprises introducing pure magnesium in a hermetically closed ladle the interior of which is subjected to a certain pressure of air or neutral gas. This process is advantageous and gives good results, but it is more particularly suitable for the treatment of small amounts of iron, for example 500-1500 kg.

Processes are also known which comprises the utilization, not of pure magnesium, but of alloys having a variable magnesium content, of the order of 5-30%. Generally ferrosilicomagnesium is employed. The disadvantage of these processes is that, for a given amount of magnesium, the cost of such an alloy is much higher than that of pure magnesium. Further, from the metallurgical point of view, if the amount of silicon that the alloy contains is excessive, it can be harmful in certain cases since it is not always desirable to introduce silicon into iron in excess of a certain amount.

The object of the invention is to provide a process for treating iron which remedies the aforementioned drawbacks and is suitable for the treatment of any amount of iron. This process is of the type in which at least one metallic inoculation product, such as pure magnesium, cerium, sodium, calcium or other suitable inoculation metal or suitable inoculation metal alloy, is introduced at the bottom of a bath of iron by means of an immersed bell, said metallic inoculating product being introduced into the bath of iron in the form of at least one piece of said product covered with a coating of a refractory material.

With this process, no violent reaction occurs at the moment of introduction of the piece or pieces of magnesium or like coated product into the iron so that it is possible to employ treating ladles of conventional type or ladles which require only low-cost adaptations. The duration of the reaction, on which the yield of the treatment depends, is prolonged as a function of the duration of consumption "Ice of the coated piece or pieces which results in a satisfactory yield at low cost.

Further features and advantages of the invention will be apparent from the ensuing description with reference to the accompanying drawings.

In the drawings:

FIG. 1 is a diagrammatic vertical sectional view of equipment for carrying out the process according to the invention;

FIGS. 2, 3 and 4 are partial detail sectional views of the bell forming part of said equipment, these views illustrating the progressive consumption of the inoculating cakes;

FIGS. 5 and 6 are views similar to FIGS. 2-4 showing a modification of the manner of carrying out the process according to the invention;

FIG. 7 is a diagrammatic sectional view of another modification of the equipment for carrying out the process according to the invention, and

FIG. 8 is a sectional view of a cake or ingot employed for the inoculation.

The invention can be carried out in accordance with two types of reactions each of which will be described in turn:

(a) The so-called reaction by stages (FIGS. 1-4), thus termed since a purality of pieces of magnesium or other metal or alloy are consumed in succession which results in a plurality of reaction stages.

(b) The so-called progressive reaction (FIGS. 5-7), thus termed since a single piece of magnesium or other metal or alloy is consumed over a rather long period of time so that the reaction, which is initially weak, is amplified in accordance with a certain progression.

In the example shown in FIG. 1, which illustrates a reaction in stages, the process according to the invention is carried out with the following equipment: a ladle or vessel 1 which has a refractory lining, contains liquid metal, for example iron F, and is closed in its upper part by a cover 2 which is merely laid on the ladle. Preferably, the ladle has great height relative to the area of its base.

The cover 2 has an opening 3 for the escape of fumes resulting from the treatment.

Extending through the cover 2 is a rod which terminates at its lower end in a treating hell or apertured container 5 having a wall provided with apertures 6. In a known manner, the bell 5 serves to introduce an amount of inoculating metal at the bottom of the ladle 1.

According to the invention, this amount of inoculating metal, which pure magnesium, is in the form of pieces of metal 7*, 7 7 coated with a coating of refractory material 8 8 8, for example of the silico-alurninous type.

The composition of such product may vary somewhat for technical or economical reasons. But it contains about 65% of silica and 22% of alumina, the balance being such elements as CaO, MgO, Fe O and Na O.

As an example, the following analysis is given:

The magnesium pieces 7 7, 7, are produced merely by breaking up small pigs or ingots of commerciallyavailable magnesium. If desired, these pigs or ingots of magnesium can be employed wholly without being broken into pieces. The pure magnesium piecesare immersed in a pulp of refractory material and dried in air. They are in this way coated with a refractory crust (8) and the 3 resulting cakes can be used once this crust has hardened.

In the embodiment shown in FIG. 1, cakes of different sizes and masses provided with different thicknesses of refractory coatings are advantageously employed. These different thicknesses are achieved by dipping the metal pieces in refractory pulps of different viscosities or by dipping them successively different numbers of times in the same pulp subsequent to intermediate drying between the successive dippings. FIG. 1 shows, from top to bottom, pieces 7 7 7 of increasing sizes coated with refractory coatings 8a, 8, 8 of increasing thicknesses.

The process is carried out in the following manner with this equipment:

The ladle 1 having been filled with liquid iron F, the cover 2 is placed on this ladle after having mounted on this cover the rod 4 and the bell 5 in which are wedged, for example, three pieces of magnesium provided with their coatings. When the cover 2 has been placed on the ladle 1, the bell 5 is located at the bottom of the ladle.

At the start, for a few seconds, no reaction occurs owing to the fact that the refractory coating of the pieces prevents the pure magnesium from coming in contact with the iron. However, the thinnest crust (8 of one (7 of the magnesium pieces heats up more rapidly and, owing to the transmission of heat through this crust, as soon as the surface temperature of the magnesium reaches the melting and @vaporizing temperature, the magnesium vaporizes and this breaks the thin crust and sets off the well-known reaction. As can be seen in comparing FIGS. 1 and 2, the smallest piece 7 at the top (FIG. 1) whose crust 8 is the first to break, is rapidly consumed in a violent reaction which lasts for about seconds. In the course of this reaction, the smallest magnesium piece 7 is rapidly vaporized and the magnesium vapor passes through the apertures 6 of the bell 5 and rises to the surface of the liquid iron F. the inoculation reaction occurs in the course of this rise through the iron F. It is advantageous that the ladle 1 have a great height so as to afford a rising path of the magnesium which is as long as possible which results in a duration of contact between the magnesium and the iron which is as long as possible. This is the first stage of the reaction.

While the first piece 7 is being consumed, the crust 8 of the piece 7 is heated more slowly since it is thicker than the crust 8 The choice of the crust thicknesses is such that it is about when consumption of the first piece 7 has finished that the magnesium of the second piece 7 is brought superficially to the melting and vaporizing temperature and its crust 8 is broken. Thus, the start of the second reaction stage follows on the end of the first.

Likewise, the third reaction stage, which corresponds to the consumption of the piece 7 having the thickest crust 8, starts at the end of the second stage, that is, after the complete melting and vaporization of the piece 7 having the crust 8 of medium thickness.

In employing three cakes of magnesium pieces coated with protective crusts of increasing thicknesses, three successive reactions are produced, each of which lasts a few seconds, the total reaction time being substantially longer than the time of the melting of pure magnesium pieces of known type uncoated with a refractory coating. This is why it is possible to obtain a very satisfactory inoculation yield by prolonging the duration of contact between the magnesium and the iron.

The start of the reaction in stages is ascertained a few seconds after the bell 5 has been placed at the bottom of the ladle 1 owing to the abundant amount of White fumes given off and the end of the treatment is revealed when the emission of fumes through the openings 3 diminishes in intensity and stops.

As a numerical example, 2 tons (French) of iron were treated with 2.4 kg. of pure magnesium consisting of a piece 7 of 700 g. coated with a refractory crust 8 having a thickness of 1 mm, a piece 7 of 800 g. coated with a retained magnesium +12/ 16 (initial R sulphurfinal sulphur) X added magnesium The coefficient 12/16 represents the ratio between the respective atomic weights of the magnesium and sulphur. If the components of this formula are replaced by their magnitudes in the considered example, there is obtained:

This yield of 29% is very satisfactory and results in spheroidal graphite cast iron under economical conditions which are much more advantageous than when ferrosilicomagnesium alloys are employed.

According to the modification shown in FIGS. 5 and 6, which illustrate the progressive reaction method, instead of employing the amount of inoculation product in the form of three pieces coated with crusts of different thickness, a single small pig 9 is employed which is coated on one of its faces with a thin refractory crust 10 and on all the other faces with a thick refractory crust 11.

Under these conditions, after having immersed the cake consisting of the pig 9 and the refractory coatings 10 and 11 at the bottom of the iron ladle, as in the foregoing example, the reaction starts with a certain delay due to the resistance to the transmission of heat of the thin refractory coating 10. But the latter is the first heated and subsequently broken when the wall of magnesium it covers has reached the melting and vaporizing temperature. Consumption of the pig 9 starts on the face thereof which was previously coated with the thin crust 10 while the other faces coated with the thick crust 11 are still in the heating stage and there is not yet transmitted to the wall of magnesium covered by this crust 11 sufficient temperature to cause the magnesium to vaporize and break the crust; the melting of the pig 9' thus progresses along a front which is roughly parallel to the face which was initially coated with the thin crust 10-. Consequently, the surface of contact between the pure magnesium and the iron is very advantageously limited to the extent of the face previously coated with the thin crust 10', which permits prolonging the reaction so that it is much less rapid and violent than if the pure magnesium had been attacked on all faces simultaneously under the usual conditions when no refractory coating is provided.

In this way, a good yield is obtained which is higher than that obtained under the conditions of the preceding example. Thus, by way of a trial, for treating 1200 kg. of iron, a pig of 1400 g. was employed which was coated on one face with a thin crust 10 having a thickness of 1 mm. and on the other faces with a thick crust 11 having a thickness of 3 mm. The reaction started 5-6 seconds after immersion of the pig at the bottom of the ladle. This time corresponds to the duration of attack of the thin crust 10 and the reaction lasted about 1 min. The yield was of the order of 32-33%.

With reference now to the embodiment shown in FIG. 7, the equipment comprises a ladle 1 which has a refractory lining and contains the liquid metal, for example iron F. This ladle is capped by a vertically extended cover 10 which increases the height of the ladle. This cover has openings 13 for the escape of fumes which result from the treatment and a refractory rod 4 extends through the cover and terminates at its lower end in a bell or com tainer provided with slots or other openings 6 allowing the escape of the vaporized magnesium.

Placed in the bell 5 is a cake mainly consisting of an inoculation piece or ingot 9, for example of pure magnesium (FIG. 8). This piece is for example produced by severing an ingot straight from casting into pieces of the desired length by means of shears, the ingot having a circular, rectangular, trapezoidal or other section.

The severed face of the piece 9 is coated with a thin refractory crust 10 and all the other faces of the ingot are coated with a thick uniform refractory crust 11 Whose thickness is 2-20 times greater than that of the thin crust 10. The refractory crusts are, for example, of silico-aluminous material having, preferably, excellent adherence characteristics when cold and when hot and an excellent resistance to mechanical and thermic shocks.

The duration of the inoculation with the progressive reaction method is variable and can be selected, in accordance with needs, between 15-20 seconds and about 2 minutes by regulating the thickness of the main coating, that is, the thickness of the thick crust 11 and by judiciously choosing the area of the cross-section receiving the thin refractory crust 10. The duration of the reaction must be as long as the layer 11 is thick. This is explained by the fact that the vaporization of the cake of magnesium 9 starts after the rapid cracking of the thin crust 10 coating the end face and increases progressively along a front parallel to this end face.

Note that for a given effective amount of magnesium, an ingot 9 of pure magnesium has a volume which is about /5 that of a piece of magnesium alloy of known type (iron, silicon, magnesium having 15% magnesium for example). Consequently, it is possible to employ a bell 5 which is shorter than the bells usually employed for the same amount of treated iron and this enables the vaporized magnesium to travel through a greater height of liquid iron up to the free surface of the iron. The yield of the treatment is thereby improved.

For example, in treating amounts of iron between 1 ton and 4 tons at a temperature of 1410 C. by means of the cake shown in FIG. 8, the yield R of magnesium is at least equal to 60% and there is obtained an iron having a graphite wholly in the spheroidal form.

It must be understood any amount of iron, that is less or more iron, can be treated in this way.

The main advantages of the invention are the following:

As can be seen, while being more progressive than the reaction produced by uncoated pure magnesium pieces of known type, the reaction produced by cakes of magnesium pieces protected by a refractory coating according to the invention remains sufficiently rapid for treating successive pouring ladles employed in mass-production casting sites.

The process is very economical since it allows the utilization of crude small pigs in the state in which they are bought with no preparation other than the breaking thereof into pieces, the classifying of the pieces into different sizes and the immersion of whole pigs and pieces in pulps of refractory materials. These operations are simple and cheap to carry out.

The small pigs can be in the form of ingots having trapezoidal faces or in the form of round-section billets. Owing to the use of treating ladles of suitable dimensions affording a suitable height of iron above the treating bell 5, an excellent inoculation yield ls achieved.

The process results in great economy as concerns the metallic inoculation product since it is employed in the pure state.

The duration of the reaction, and therefore the yield, can be controlled by employing cakes of magnesium having refractory crusts of suitably diminishing thickness, as in the first embodiment, or by employing a single ingot having a suitable mass and a thin crust 10 on a small part of its outer surface and a thick crust 11 on the rest of its surface, as in the second embodiment.

It is possible to control not only the duration but also the progressivity of the treatment and therefore achieve a satisfactory yield while attenuating the violence of the reaction without utilization of special and costly equipment.

Although specific embodiments of the invention have been described, many modifications and changes may be made therein without departing from the scope of the invention as defined in the appended claims.

Thus, it is possible to employ cakes of magnesium coated with a refractory coating in accordance with the invention in special ladles of known type allowing a treatment in a retort under pressure, which considerably increases the yield of the treatment, that is, the yield of magnesium relative to treatments in these same special ladles with pure magnesium uncoated with a refractory coating.

Further, the two types of reaction, namely the reaction in stages and the progressive reaction, can be employed simultaneously in combination, by employing a single pig 9, such as that shown in FIG. 5, and a plurality of cakes 7, such as those shown in FIG. 1, to make up the weight of magnesium necessary for the treatment of a given amount of iron.

'Further, instead of employing silicoaluminous refractory coatings or coatings containing refractory clay, it is possible to employ refractory coatings containing silica or asbestos.

The invention is also applicable to the treatment of iron with cerium or alkali metals, such as sodium and calcium, and to the treatment of iron with metal alloys, such as misch metal. The invention permits the staggering of reactions by, for example, reacting in accordance with a preferential order metals and/or metal alloys by coating the pieces which must react first with a thinner refractory coating and the pieces which must react last with a thicker coating.

It must be understood that the process can be carried out by putting the pieces of magnesium coated with a refractory crust in contact with the iron by means of any device other than the bell 5.

Having 'now described my invention what I claim as new and desire to secure by Letters Patent is:

1. A process for treating liquid iron comprising introducing an amount of at least one metallic inoculation product at the bottom of a bath of iron by means of an apertured container held immersed, said amount of inoculating product being totally covered with a coating of a non-metallic refractory material before immersion in the bath and being in the form of at least one solid piece of said product, said coating having at least one part which is thinner than a remaining part of said coating, so that a part of said amount of inoculation product covered by said thinner part :of said coating comes in contact with said liquid iron before another part of said amount of inoculation product whereby said inoculation product comes into contact with said liquid metal in a progressive manner and the duration of contact is prolonged.

2. A process for treating liquid iron comprising introducing an amount of at least one metallic inoculation product selected from the group consisting of pure magnesium, cerium, sodium, calcium, a suitable inoculation metal, a suitable inoculation metal alloy, at the bottom of a bath of iron by means of an apertured container held immersed at the end of a rod, said amount of inoculating product being totally covered with a coating of a non-metallic refractory material before immersion in the bath and being in the form of at least one solid piece of said product, said coating having at least one part which is thinner than a remaining part of said coating, so that a part of said amount of inoculation product covered by said thinner part of said coating comes in contact with said liquid iron before another part of said amount of inoculation product whereby said inoculation product comes into contact with said liquid metal in a progressive manner and the duration of contact is prolonged.

3. A process for treating liquid iron, comprising introducing at the bottom of a bath of liquid iron by means of an apertured container held immersed a plurality of pieces of at least one metallic inoculation product wholly coated with non-metallic refractory coatings of different thicknesses before immersion in the bath so that said pieces melt successively in the form of a reaction in stages proceeding in the order of the increasing thicknesses of the refractory coatings.

4. A process for treating liquid iron, comprising introducing att he bottom of a bath of liquid iron by means of an apertured container held immersed at least one piece of at least one metallic inoculation product wholly coated with a non-metallic refractory coating before immersion in the bath, said piece having one face on which said refractory coating is thin, and other faces on which a. much thicker refractory coating is employed, so that said piece of inoculation product melts progressively along a front which is roughly parallel to said face of the piece initially coated with said thin coating.

5. A process as claimed in claim 4, employing a piece of inoculation product on which the thickness of said thick coating is 2-20 times thicker than that of said thin coating.

6. A process as claimed in claim 3, comprising employing, in addition to said plurality of pieces of inoculation 8 product, a further piece of inoculation product wholly coated with a non-metallic refractory coating, said further piece of inoculation product having a face with a thin refractory coating and other faces with much thicker refractory coatings.

7. A process as claimed in claim 1, wherein said nonmetallic refractory coating has good adherence in the hot and cold state to the subjacent inoculation product and resists mechanical and thermic shocks.

8. A process as claimed in claim 1, comprising employing a plurality of coated pieces of dilferent inoculation metals.

9. A process as claimed in claim 1, comprising employing a plurality of coated pieces of different inoculation metal alloys.

References Cited UNITED STATES PATENTS 3,151,975 10/1964 Madaras 75-l29X 3,231,368 1/1966 Watson 75-l3OX 3,459,541 8/1969 Hohl 75-430 L. DEWAYNE RUTLEDE, Primary Examiner J. E. LEGRU, Assistant Examiner US. Cl. X.R. 75-129 

